Part 2: Forensic attribution profiling of Russian VX in food using liquid chromatography-mass spectrometry

Use of carbonyldiimidazole as a derivatization agent for the detection of pinacolyl alcohol, a forensic marker for Soman, by EI-GC-MS and LC-HRMS in official OPCW proficiency test matrices

Pinacolyl alcohol (PA), a key forensic marker for the nerve agent Soman (GD), is a particularly difficult analyte to detect by various analytical methods. In this work, we have explored the reaction between PA and 1,1'-carbonyldiimidazole (CDI) to yield pinacolyl 1H-imidazole-1-carboxylate (PIC), a product that can be conveniently detected by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Regarding its GC-MS profile, this new carbamate derivative of PA possesses favorable chromatographic features such as a sharp peak and a longer retention time (RT = 16.62 min) relative to PA (broad peak and short retention time, RT = 4.1 min). The derivative can also be detected by LC-HRMS, providing an avenue for the analysis of this chemical using this technique where PA is virtually undetectable unless present in large concentrations. From a forensic science standpoint, detection of this low molecular weight alcohol signals the past or latent presence of the nerve agent Soman (GD) in a given matrix (i.e., environmental or biological). The efficiency of the protocol was tested separately in the analysis and detection of PA by EI-GC-MS and LC-HRMS when present at a 10 μg/mL in a soil matrix featured in the 44th PT and in a glycerol-rich liquid matrix featured in the 48th Official Organization for the Prohibition of Chemical Weapons (OPCW) Proficiency Test when present at a 5 μg/mL concentration. In both scenarios, PA was successfully transformed into PIC, establishing the protocol as an additional tool for the analysis of this unnatural and unique nerve agent marker by GC-MS and LC-HRMS.

Chemical, Physical, and Toxicological Properties of V-Agents

V-agents are exceedingly toxic organophosphate nerve agents. The most widely known V-agents are the phosphonylated thiocholines VX and VR. Nonetheless, other V-subclasses have been synthesized. Here, a holistic overview of V-agents is provided, where these compounds have been categorized based on their structures to facilitate their study. A total of seven subclasses of V-agents have been identified, including phospho(n/r)ylated selenocholines and non-sulfur-containing agents, such as VP and EA-1576 (EA: Edgewood Arsenal). Certain V-agents have been designed through the conversion of phosphorylated pesticides to their respective phosphonylated analogs, such as EA-1576 derived from mevinphos. Further, this review provides a description of their production, physical properties, toxicity, and stability during storage. Importantly, V-agents constitute a percutaneous hazard, while their high stability ensures the contamination of the exposed area for weeks. The danger of V-agents was highlighted in the 1968 VX accident in Utah. Until now, VX has been used in limited cases of terrorist attacks and assassinations, but there is an increased concern about potential terrorist production and use. For this reason, studying the chemistry of VX and other less-studied V-agents is important to understand their properties and develop potential countermeasures.

Benzyl trichloroacetimidates as derivatizing agents for phosphonic acids related to nerve agents by EI-GC-MS during OPCW proficiency test scenarios

The use of benzyl trichloroacetimidates for the benzylation of phosphonic acid nerve agent markers under neutral, basic, and slightly acidic conditions is presented. The benzyl-derived phosphonic acids were detected and analyzed by Electron Ionization Gas Chromatography-Mass Spectrometry (EI-GC-MS). The phosphonic acids used in this work included ethyl-, cyclohexyl- and pinacolyl methylphosphonic acid, first pass hydrolysis products from the nerve agents ethyl N-2-diisopropylaminoethyl methylphosphonothiolate (VX), cyclosarin (GF) and soman (GD) respectively. Optimization of reaction parameters for the benzylation included reaction time and solvent, temperature and the effect of the absence or presence of catalytic acid. The optimized conditions for the derivatization of the phosphonic acids specifically for their benzylation, included neutral as well as catalytic acid (< 5 mol%) and benzyl 2,2,2-trichloroacetimidate in excess coupled to heating the mixture to 60 °C in acetonitrile for 4 h. While the neutral conditions for the method proved to be efficient for the preparation of the p-methoxybenzyl esters of the phosphonic acids, the acid-catalyzed process appeared to provide much lower yields of the products relative to its benzyl counterpart. The method's efficiency was tested in the successful derivatization and identification of pinacolyl methylphosphonic acid (PMPA) as its benzyl ester when present at a concentration of ~ 5 μg/g in a soil matrix featured in the Organisation for the Prohibition of Chemical Weapons (OPCW) 44th proficiency test (PT). Additionally, the protocol was used in the detection and identification of PMPA when spiked at ~ 10 μg/mL concentration in a fatty acid-rich liquid matrix featured during the 38^th OPCW-PT. The benzyl derivative of PMPA was partially corroborated with the instrument's internal NIST spectral library and the OPCW central analytical database (OCAD v.21_2019) but unambiguously identified through comparison with a synthesized authentic standard. The method's MDL (LOD) values for the benzyl and the p-methoxybenzyl pinacolyl methylphosphonic acids were determined to be 35 and 63 ng/mL respectively, while the method's Limit of Quantitation (LOQ) was determined to be 104 and 189 ng/mL respectively in the OPCW-PT soil matrix evaluated.

Chemical forensic profiling and attribution signature determination of sarin nerve agent using GC-MS, LC-MS and NMR

Sarin is a highly toxic nerve agent classified by the Chemical Weapon Convention as a Schedule 1 chemical with no use other than to kill or injure. Moreover, in recent times, chemical warfare agents have been deployed against both military and civilian populations. Chemical warfare agents always contain minor impurities that can provide important chemical attribution signatures (CAS) that can aid in forensic investigations. In order to understand the trace molecular composition of sarin, various analytical approaches including GC-MS, LC-MS and NMR were used to determine the chemical markers of a set of sarin samples. Precursor materials were studied and the full characterisation of a synthetic process was undertaken in order to provide new insights into potential chemical attribution signatures for this agent. Several compounds that were identified in the precursor were also found in the sarin samples linking it to its method of preparation. The identification of these CAS contributes critical information about a synthetic route to sarin, and has potential for translation to related nerve agents.

Forensic signatures of a chemical weapon precursor DMPADC for determination of a synthetic route

Chemical forensics has been widely recognized as an important tool to investigate alleged use of chemical weapons and/or to identify the illicit production of chemical warfare agents. This paper describes the use of gas chromatography and mass spectrometry (GC-MS) to determine chemical attribution signatures (CAS) N,N-dimethylphosphoramidic dichloride (DMPADC), a key precursor of tabun, for tracking the production of tabun. Synthetic samples were identified and classified by using GC-MS and chemometrics. Analysis samples (n = 27) were collected from three synthetic DMPADC routes; 20 potential CAS were identified, and the structures of five CAS were assigned. Principal component analysis (PCA) was performed to summarize the distribution trend of the samples and to check for the presence of outliers. A Partial least squares discriminant analysis (PLSDA) model was established to discriminate and classify the synthetic samples. The proposed model in this paper has high predictive ability, and the test set samples can be correctly categorized.

Analysis of Organophosphorus-Based Nerve Agent Degradation Products by Gas Chromatography-Mass Spectrometry (GC-MS): Current Derivatization Reactions in the Analytical Chemist's Toolbox

The field of gas chromatography-mass spectrometry (GC-MS) in the analysis of chemical warfare agents (CWAs), specifically those involving the organophosphorus-based nerve agents (OPNAs), is a continually evolving and dynamic area of research. The ever-present interest in this field within analytical chemistry is driven by the constant threat posed by these lethal CWAs, highlighted by their use during the Tokyo subway attack in 1995, their deliberate use on civilians in Syria in 2013, and their use in the poisoning of Sergei and Yulia Skripal in Great Britain in 2018 and Alexei Navalny in 2020. These events coupled with their potential for mass destruction only serve to stress the importance of developing methods for their rapid and unambiguous detection. Although the direct detection of OPNAs is possible by GC-MS, in most instances, the analytical chemist must rely on the detection of the products arising from their degradation. To this end, derivatization reactions mainly in the form of silylations and alkylations employing a vast array of reagents have played a pivotal role in the efficient detection of these products that can be used retrospectively to identify the original OPNA.

Gas Chromatography-Mass Spectrometry Analysis of Synthetic Opioids Belonging to the Fentanyl Class: A Review

The rising number of deaths caused by fentanyl overdosing in the US due to the overwhelming illicit use of this synthetic opioid has started a global campaign to develop efficient ways to control its production and distribution as well as discovering efficient antidotes to mitigate its lethal effects. Another important vein of focused research established by various agencies lies in the development of efficient and practical protocols for the detection of this opioid and analogs thereof in various matrices, whether environmental or biological in nature, particularly in the field of gas chromatography-mass spectrometry (GC-MS). The following review will cover the literature dealing with the detection and identification of synthetic opioids belonging to the fentanyl class by GC-MS means and hyphenated versions of the technique. Detailed descriptions will be given for the GC-MS methods employed for the analysis of the opioid, starting with the nature of the extraction protocol employed prior to analysis to the actual findings presented by the cited reports. Great effort has gone into describing the methods involved in each paper in a detailed manner and these have been compiled by year in tables at the end of each section for the reader's convenience. Lastly, the review will end with concluding remarks about the state of GC-MS analysis with regards to these powerful opioids and what lies ahead for this analytical field.

Mass spectrometric analysis of adducts of sulfur mustard analogues to human plasma proteins: approach towards chemical provenancing in biomedical samples

The primary aim of this study was to identify biomarkers of exposure to some so-called Schedule 1 sulfur mustard (HD) analogues, in order to facilitate and expedite their retrospective analysis in case of alleged use of such compounds. Since these HD analogues can be regarded as model compounds for possible impurities of HD formed during synthesis processes, the secondary aim was to explore to which extent these biomarkers can be used for chemical provenancing of HD in case biomedical samples are available. While the use of chemical attribution signatures (CAS) for neat chemicals or for environmental samples has been addressed quite frequently, the use of CAS for investigating impurities in biomedical samples has been addressed only scarcely. Human plasma was exposed to each of the five HD analogues. After pronase or proteinase K digestion of precipitated protein and sample work-up, the histidine (His) and tripeptide (CPF) adducts to proteins were analyzed, respectively. Adducts of the analogues could still be unambiguously identified next to the main HD adducts in processed plasma samples after exposure to HD mixed with each of the analogues, at a 1% level relative to HD. In conclusion, we have identified plasma protein adducts of a number of HD analogues, which can be used as biomarkers to assess an exposure to these Schedule 1 chemicals. We have shown that adducts of these analogues can still be analyzed after work-up of plasma samples which had been exposed to these analogues in a mixture with HD, supporting the hypothesis that biomedical sample analysis might be useful for chemical provenancing.

Route Determination of Sulfur Mustard Using Nontargeted Chemical Attribution Signature Screening

Route determination of sulfur mustard was accomplished through comprehensive nontargeted screening of chemical attribution signatures. Sulfur mustard samples prepared via 11 different synthetic routes were analyzed using gas chromatography/high-resolution mass spectrometry. A large number of compounds were detected, and multivariate data analysis of the mass spectrometric results enabled the discovery of route-specific signature profiles. The performance of two supervised machine learning algorithms for retrospective synthetic route attribution, orthogonal partial least squares discriminant analysis (OPLS-DA) and random forest (RF), were compared using external test sets. Complete classification accuracy was achieved for test set samples (2/2 and 9/9) by using classification models to resolve the one-step routes starting from ethylene and the thiodiglycol chlorination methods used in the two-step routes. Retrospective determination of initial thiodiglycol synthesis methods in sulfur mustard samples, following chlorination, was more difficult. Nevertheless, the large number of markers detected using the nontargeted methodology enabled correct assignment of 5/9 test set samples using OPLS-DA and 8/9 using RF. RF was also used to construct an 11-class model with a total classification accuracy of 10/11. The developed methods were further evaluated by classifying sulfur mustard spiked into soil and textile matrix samples. Due to matrix effects and the low spiking level (0.05% w/w), route determination was more challenging in these cases. Nevertheless, acceptable classification performance was achieved during external test set validation: chlorination methods were correctly classified for 12/18 and 11/15 in spiked soil and textile samples, respectively.

Methylation protocol for the retrospective detection of isopropyl-, pinacolyl- and cyclohexylmethylphosphonic acids, indicative markers for the nerve agents sarin, soman and cyclosarin, at low levels in soils using EI-GC-MS

A practical and efficient protocol for the derivatization and detection by GC-EI-MS of isopropyl-, pinacolyl- and cyclohexylmethylphosphonic acids, key diagnostic degradation products of the nerve agents sarin, soman and cyclosarin respectively, in six different types of soil matrices is presented. The method involves the in situ conversion of the phosphonic acids to their respective methyl esters using trimethyloxonium tetrafluoroborate when present in the soils at low levels (10 μg g^-1) without any prior extractions or soil preparation. The soils employed in our study were Nebraska EPA soil, Georgia soil, silt, Virginia type A soil, regular sand and Ottawa sand and were chosen for their vast differences in composition and physical features. Appealing attributes of the protocol include its rapidity (t < 30 min), mildness (ambient temperature), and practicality that includes the production of the phosphonic methyl esters that can be easily detected by GC-EI-MS and corroborated with the instrument's internal NIST spectral library or the Organisation for the Prohibition of Chemical Weapons (OPCW) central analytical database (OCAD v.21_2019). The overall efficacy of the protocol was then tested on a soil sample featured in the 44th OPCW PT that our laboratory participated in. After preparing the soil so as to give pinacolyl methylphosphonic acid at a 5 μg g^-1 concentration, the acid was successfully methylated and detected by GC-EI-MS. The protocol's performance mirrors that of the universally employed diazomethane protocol but accomplishes this without any of the explosive hazards and time consuming reagent preparation commonly associated with it.

Part 3: Solid phase extraction of Russian VX and its chemical attribution signatures in food matrices and their detection by GC-MS and LC-MS

Chemical attribution signatures indicative of O-isobutyl S-(2-diethylaminoethyl) methylphosphonothioate (Russian VX) synthetic routes were investigated in spiked food samples. Attribution signatures were identified using a multifaceted approach: Russian VX was synthesized using six synthetic routes and the chemical attribution signatures identified by GC-MS and LC-MS. Three synthetic routes were then down selected and spiked into complex matrices: bottled water, baby food, milk, liquid eggs, and hot dogs. Sampling and extraction methodologies were developed for these materials and used to isolate the attribution signatures and Russian VX from each matrix. Recoveries greater than 60% were achieved for most signatures in all matrices; some signatures provided recoveries greater than 100%, indicating some degradation during sample preparation. A chemometric model was then developed and validated with the concatenated data from GC-MS and LC-MS analyses of the signatures; the classification results of the model were > 75% for all samples. This work is part three of a three-part series in this issue of the United States-Sweden collaborative efforts towards the understanding of the chemical attribution signatures of Russian VX in crude materials and in food matrices.

Part 1: Tracing Russian VX to its synthetic routes by multivariate statistics of chemical attribution signatures

Chemical attribution signatures (CAS) associated with different synthetic routes used for the production of Russian VX (VR) were identified. The goal of the study was to retrospectively determine the production method employed for an unknown VR sample. Six different production methods were evaluated, carefully chosen to include established synthetic routes used in the past for large scale production of the agent, routes involving general phosphorus-sulfur chemistry pathways leading to the agent, and routes whose main characteristic is their innate simplicity in execution. Two laboratories worked in parallel and synthesized a total of 37 batches of VR via the six synthetic routes following predefined synthesis protocols. The chemical composition of impurities and byproducts in each route was analyzed by GC/MS-EI and 49 potential CAS were recognized as important markers in distinguishing these routes using Principal Component Analysis (PCA). The 49 potential CAS included expected species based on knowledge of reaction conditions and pathways but also several novel compounds that were fully identified and characterized by a combined analysis that included MS-CI, MS-EI and HR-MS. The CAS profiles of the calibration set were then analyzed using partial least squares discriminant analysis (PLS-DA) and a cross validated model was constructed. The model allowed the correct classification of an external test set without any misclassifications, demonstrating the utility of this methodology for attributing VR samples to a particular production method. This work is part one of a three-part series in this Forensic VSI issue of a Sweden-United States collaborative effort towards the understanding of the CAS of VR in diverse batches and matrices. This part focuses on the CAS in synthesized batches of crude VR and in the following two parts of the series the influence of food matrices on the CAS profiles are investigated.